1^0 ESSAYS AND OBSERVATIONS 



We have already fhewn by experiment, 

 that magnefia alba is a compound of a pecu- 

 liar earth and fixed air. When this fubftance 

 is mixed with lime-water, the lime (hews a 

 Wronger attraftion for fixed air than that of 

 the earth of magnefia ; the air leaves this 

 powder to join itfelf to the lime. And as 

 neither the lime when faturated with air, 

 nor the magnefia when deprived of it, are 

 foluble in water, the lime-water becomes per- 

 fedly pure and infipid, the lime which: it 

 contained being mixed with the magnefia. 

 But if the magnefia be deprived of air by cal- 

 cination before it is mixed with the lime- 

 water, this fluid fufFers no alteration. 



If quick-lime be mixed with a difiblved 

 alkali, it likeways fhews an attradion for 

 fixed air fuperior to that of the alkali. It 

 robs this fait of its air, and thereby becomes 

 Oiild itfelf, while the alkali is consequently 

 rendered more corrofive, or difcovers its na- 

 tural degree of acrimony or fi:rong attraction 

 for water, and for bodies of the inflammable, 

 and of the animal and vegetable kind; which 

 attradion was lefs perceivable as long as it 

 v\^as faturated with air. And the volatile 

 ^Ik^li when deprived of its air, befides this 



attradtior^ 



